Non-surface Activity and Micellization Behavior of Cationic Amphiphilic Block Copolymer Synthesized by Reversible Addition–Fragmentation Chain Transfer Process

Abstract

Cationic amphiphilic diblock copolymers of poly(n-butylacrylate)-b-poly(3-(methacryloylamino)propyl)trimethylammonium chloride) (PBA-b-PMAPTAC) with various hydrophobic and hydrophilic chain lengths were synthesized by a reversible addition-fragmentation chain transfer (RAFT) process. Their molecular characteristics such as surface activity/nonactivity were investigated by surface tension measurements and foam formation observation. Their micelle formation behavior and micelle structure were investigated by fluorescence probe technique, static and dynamic light scattering (SLS and DLS), etc., as a function of hydrophilic and hydrophobic chain lengths. The block copolymers were found to be non-surface active because the surface tension of the aqueous solutions did not change with increasing polymer concentration. Critical micelle concentration (cmc) of the polymers could be determined by fluorescence and SLS measurements, which means that these polymers form micelles in bulk solution, although they were non-surface active. Above the cmc, the large blue shift of the emission maximum of N-phenyl-1-naphthylamine (NPN) probe and the low micropolarity value of the pyrene probe in polymer solution indicate the core of the micelle is nonpolar in nature. Also, the high value of the relative intensity of the NPN probe and the fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene (DPH) probe indicated that the core of the micelle is highly viscous in nature. DLS was used to measure the average hydrodynamic radii and size distribution of the copolymer micelles. The copolymer with the longest PBA block had the poorest water solubility and consequently formed micelles with larger size while having a lower cmc. The "non-surface activity" was confirmed for cationic amphiphilic diblock copolymers in addition to anionic ones studied previously, indicating the universality of non-surface activity nature.

Near-Infrared Dye-Conjugated Amphiphilic Hyaluronic Acid Derivatives as a Dual Contrast Agent for In Vivo Optical and Photoacoustic Tumor Imaging

“…The measurement was conducted according to the reported method. 44 The results are summarized in the SI.…”

Why Ionic Amphiphilic “Block” Copolymer Can Be Non-surface Active? Comparison of Homopolymer, Block and Random Copolymers of Poly(styrenesulfonate)

“…All three polymers are ionic polymers, with properties largely affected by image charge repulsion at the air/water interface, but only the block copolymer can become non-surface active, which means that micelle formation should play an important role as the origin of non-surface activity although an image charge effect is the primary origin of the non-surface activity. 7,9 The adsorbed state of the block copolymer should be largely destabilized by image charge repulsion, but this repulsion is not strong enough to repell block copolymers from the water surface. Hence, the homopolymer shows slight surface activity and the random copolymer is surface active.…”

Investigation of dual-sensitive nanogels based on chitosan andN-isopropylacrylamide and its intelligent drug delivery of 10-hydroxycamptothecine

“…The CAC was determined by fluorescence probe method (Liu et al, 2009;Ghosh et al, 2011;Vasilescu et al, 2011). Briefly, the nanogels with concentrations ranged from 1.5 Â 10 À3 to 1.5 mg/mL, were added into the volumetric flasks containing pyrene with final concentration of 6 Â 10 À7 M. Then, the solutions were sonicated for 30 min followed by incubation at 40 C for 1 h and kept from light overnight at R.T. Fluorescence spectra were recorded with an RF-5301 PC fluorescence spectrophotometer (Shimadzu, Tokyo, Japan) with the emission wavelength at 390 nm.…”

“…As detailed by many authors (Liu et al, 2009;Ghosh et al, 2011;Vasilescu et al, 2011), pyrene fluorescence probe method was widely employed to estimate hydrophobic microenvironments within micelles in aqueous medium from the fluorescent excitation spectra of pyrene. At low concentration of the di-block copolymer, a shift of the excitation band at 334 nm is negligible.…”